1. Field of the Invention
The present invention relates to technology for suppressing ESD (also called electrostatic discharge damage) of a semiconductor integrated circuit chip mounted on an IC card. More particularly, the invention relates to technology that can be effectively adapted to memory cards such as multi-media cards.
2. Prior Art
A variety of memory cards have heretofore been provided for storing multi-media data in compact sizes having decreased weights. For example, there has been provided a multi-media card having a memory and a memory controller mounted on a card substrate, establishing an interface to a host unit using a small number of signals.
Giving priority to a small size and reduced weight, the memory card of this type has the connection terminals for connection to the host unit, the connection terminals being exposed on the card substrate, but has no particular mechanism such as cover for protecting the terminals. When the exposed terminals are touched at the time when the memory card is removed from the host unit, therefore, a semiconductor integrated circuit chip connected to the exposed terminals may be damaged. Usually, the semiconductor integrated circuit chip is provided with an input protection circuit for preventing the input circuit from the electrostatic damage. The input protection circuit is constituted by, for example, disposing, between an input terminal and a power source terminal, an element such as a diode whose connection state is reversed relative to the amplitude voltage of the input signal. It is, however, expected that the memory card is carried by itself and is frequently attached to, and detached from, the host unit. Thus, the present inventors have found the importance of reinforcing the prevention of the electrostatic damage.
Though the technical field is different from the above memory card, Japanese Patent Laid-Open No. 209379/1998 discloses technology for reinforcing the protection of input against the electrostatic damage. According to this technology, a metal wiring layer is formed maintaining a gap (discharge gap) in which static electricity could be discharged relative to an electrode layer on a semiconductor substrate so that when static electricity has entered into the electrode layer, the static electricity is discharged to the metal wiring layer, preventing the static electricity that has entered into the electrode layer from entering into the semiconductor element. Further, Japanese Patent Laid-Open No. 271937/1995 discloses a circuit employing a gate-source protection diode of a MOSFET that is externally attached to a semiconductor integrated circuit chip to prevent the electrostatic damage.
There has further been provided a varistor of semiconductor ceramics from the standpoint of protecting the circuitry from an overvoltage.
The present inventors have forwarded the following study from the standpoint reinforcing the prevention of electrostatic damage of the IC card such as a memory card having connection terminals that are exposed.
First, it became obvious that when Zener diodes of a large size are integrated on a semiconductor integrated circuit chip to obtain an energy withstand amount that helps reinforce the prevention of electrostatic damage, the area efficiency decreases in the midst of fine circuit elements, driving up the cost to a conspicuous degree.
Second, when an element for protection from an overvoltage is attached to the semiconductor integrated circuit chip to reinforce the prevention of electrostatic damage, the efficiency for preventing the electrostatic damage does not increase unless consideration is given to a relationship between the characteristics and the ability of the overvoltage protection circuit incorporated in the semiconductor integrated circuit chip. Besides, the externally attached circuit elements that are large in size or that are large in number, cause an increase in the size and thickness of the IC card. Such a viewpoint has not been taught by the above prior art. In this specification, the overvoltage stands for a surge voltage or a transient voltage that generates electrostatically.
Third, even when the countermeasure against the electrostatic damage is taken by using the externally attached circuit elements, there is no guarantee that the device is absolutely safe from the damage when it is handled in an unexpected manner by a person who is not familiar with. It is therefore necessary to make perfection more perfect.
Fourth, even when the input circuit of the semiconductor integrated circuit is electrostatically damaged, it can be expected that the data in the memory remain safe. In such a case, recovering the data from the memory card gives an excellent feature relieving the data and offering an increased safety of the memory card as a storage medium.
Fifth, a countermeasure against the electrostatic damage by the externally attached circuit elements, decreases, at least, the vacant region on the card substrate correspondingly. Even in this case, it becomes necessary to avoid concentration of wiring patterns and the concentration of bonding wires that could become a cause of malfunction due to undesired leakage of signal lines. This contrivance is necessary even when the memory capacity of the memory card is to be increased.
The present invention provides an IC card capable of reinforcing the prevention of electrostatic damage without driving up the cost of the semiconductor integrated circuit chip.
The present invention further provides an IC card capable of reinforcing the prevention of electrostatic damage by attaching overvoltage protection elements to the semiconductor integrated circuit chip without causing a great change in the size and thickness of the card.
The invention further provides an IC card which can be expected to prevent electrostatic damage caused by an unexpected handling by a person who is not familiar with.
The invention further provides an IC card capable of easily recovering the data in the memory card even when the input circuit of the semiconductor integrated circuit chip is electrostatically damaged, provided the data in the memory remain safe.
The invention further provides an IC card capable of avoiding the concentration of wiring patterns and bonding wires that could cause a malfunction due to undesired leakage of signal lines even when the vacant region on the card substrate is decreased by the countermeasure against the electrostatic damage by externally attaching the circuit elements.
The invention further provides an IC card having a relatively large storage capacity in a relatively small size.
The above and other objects as well as novel features of the present invention will become obvious from the description of the specification and the accompanying drawings.
Briefly described below are representative examples of the invention disclosed in this application.
[1] Second overvoltage protection elements capable of reinforcing the prevention of electrostatic damage are externally attached to the semiconductor integrated circuit chip by taking into consideration a relationship to first overvoltage protection elements that are integrated in a semiconductor integrated circuit chip. That is, an IC card has a semiconductor integrated circuit chip mounted on a card substrate and plural connection terminals that are exposed, wherein the connection terminals are connected to predetermined external terminals of the semiconductor integrated circuit chip, the first overvoltage protection elements connected to the external terminals are integrated on the semiconductor integrated circuit chip, and the second overvoltage protection elements connected to the connection terminal are mounted on the card substrate.
According to a first aspect, the second overvoltage protection elements are variable resistor elements having a current tolerating ability greater than that of the first overvoltage protection elements.
According to a second aspect, a voltage greater than a rated voltage applied to the second overvoltage protection elements for flowing a specified pulse current, is the voltage that enables the first overvoltage protection elements to flow only a current smaller than the above specifued pulse current.
According to a third aspect, the second overvoltage protection elements are variable resistor elements having a breakdown voltage larger than that of the first overvoltage protection elements.
According to a fourth aspect, the second overvoltage protection elements have a capacity larger than that of the first overvoltage protection elements.
This enables a high-speed surge pulse to be by-passed through a low resistance.
According to a fifth aspect, the second overvoltage protection elements have a breakdown voltage smaller than a breakdown voltage of the first overvoltage protection elements.
According to a sixth aspect, the second overvoltage protection elements has a breakdown voltage smaller than a breakdown voltage of a circuit that is protected by the first overvoltage protection elements.
In any aspect, it can be said that the second overvoltage protection elements exhibit the effect for preventing the electrostatic damage, since consideration has been given to a relationship between the characteristics and the ability of the first overvoltage protection elements that are contained in the semiconductor integrated circuit chip.
The second overvoltage protection elements may have their ends on one side thereof connected to the power source connection terminals of the card substrate and may have their ends on the other side thereof connected to the signal connection terminals. The signal connection terminals are connected to the corresponding external terminals of the semiconductor integrated circuit chip. Here, the signal propagation distances from the signal connection terminals to the corresponding second overvoltage protection elements are shorter than the signal propagation distances from the signal connection terminals to the corresponding external terminals of the semiconductor integrated circuit chip. This prevents the semiconductor integrated circuit chip from being directly affected destructively by the overvoltage before the second overvoltage protection elements work in response to the overvoltage.
The second overvoltage protection elements may be varistors of the surface-mount type comprising chiefly semiconductor ceramics, an array of chip diodes, chip capacitors or chip transistors. This makes it possible to decrease the mounting area or the occupation area of the second overvoltage protection elements. The surface mounting lowers the cost of production.
When a memory card such as a multi-media card is used as an IC card, the semiconductor chip is a controller chip, and one or plural memory chips (e.g., nonvolatile memory chips) connected to the controller chip are further mounted on the card substrate. The controller chip has a memory control function for controlling the reading/writing operation for the memory chips according to an instruction from an external unit.
When a consideration is given to data security and copyright, the controller chip may employ a privacy protection function for effecting the encryption for the data written into the memory chip and for effecting the decryption for the data read out from the memory chip.
When a consideration is given to preventing the electrostatic damage even during the steps of manufacturing the IC card, the second overvoltage protection elements connected to the connection terminals should be mounted on the card substrate, first, and, then, predetermined external terminals of the semiconductor integrated circuit chip should be connected to the connection terminals. Then, the protection by the second overvoltage protection elements is obtained in a step of connecting the semiconductor integrated circuit chip.
[2] The invention is concerned with an IC card having a semiconductor integrated circuit chip mounted on a card substrate, wherein plural connection terminals are exposed, predetermined external terminals of said semiconductor integrated circuit chip are connected to the connection terminals, first overvoltage protection elements connected to the external terminals are integrated on the semiconductor integrated circuit chip, and second overvoltage protection elements connected to the connection terminals are mounted on the card substrate, and wherein the second overvoltage protection elements may be connected by being surface-mounted on the electrically conducting pattern formed on the card substrate. This makes it possible to decrease the cost of mounting the second overvoltage protection elements.
When a memory card such as a multi-media card is used as the IC card, the semiconductor chip is a controller chip, and one or plural memory chips connected to the controller chip are further mounted on the card substrate. Here, bonding wires are used for connecting the connection terminals to the external terminals of the controller chip, and bonding wires are used for connecting the controller chip to the memory chips. Therefore, a number of wiring patterns having the same function as the connection by the bonding wires, need not be densely formed on the card substrate. Space on the controller chip or the memory chips can be used for the wiring. Accordingly, this contributes to decreasing the cost of the card substrate.
When plural memory chips are to be connected in parallel to the controller chip by bonding wires, the memory chips may be mounted on the card substrate in a manner that the chips are stacked one upon the other with their positions being so deviated that the external terminals are exposed, from the standpoint of shortening the lengths of the bonding wires. Therefore, the distance to the controller chip is shortened and the lengths of the bonding wires are shortened compared to when the memory chips are arranged without being stacked one upon the other. This decreases the probability of undesired contact or breakage of the bonding wires. In this case, in particular, a condition should be maintained in that the area on one surface of the card substrate is larger than the total areas of the memory chips and of the controller chip. This is to provide the card substrate with extra space for sufficiently coping with a restrictive condition in that the wiring layer is formed on one surface only of the card substrate. This is not a simple idea of mounting the memory chips in a stacked manner for decreasing the area of the card substrate.
[3] The invention is concerned with an IC card in which plural memory chips and the controller chip for controlling the memory chips are mounted on one surface of the card substrate, wherein when the memory chips are mounted on the card substrate in a manner of being stacked one upon the other with their positions being so deviated that the external terminals are exposed, the external terminals of the memory chips that receive the same signals from the controller chip are successively connected in series by bonding the wires. The bonding method of a so-called stitch sewing is employed. The bonding wires can be shortened as a whole compared to when the controller chip is connected to the external terminals through the bonding wires. In this respect, too, the probability of undesired contact or breakage of lines due to the concentration of the bonding wires can be decreased.
The invention is concerned with an IC card in which plural memory chips and the controller chip for controlling the memory chips are mounted on one surface of the card substrate, wherein when the memory chips are mounted on the card substrate in a manner of being stacked one upon the other with their positions being so deviated that the external terminals are exposed, the external terminals for receiving chip selection signals of the memory chips are located at the ends of the arrangements of the external terminals of the nonvolatile memory chips, and are connected to the controller chip by bonding the wires. In a constitution for separately selecting the plural memory chips, the external terminals for receiving the chip selection signals must be separately connected to the external terminals for outputting the chip selection signal of the controller chip. Therefore, the above stitch-bonding method cannot be employed. However, the external terminals for selecting the chips are arranged at the ends of the memory chips and work to accomplish necessary connection without hindered by other bonding wires.
[4] The memory chips and the controller chip mounted on the card substrate may be arranged in the form of columns. That is, the memory chips are connected to the controller chip, the connection terminals formed on the card substrate are connected to predetermined external terminals of the controller chip, the first overvoltage protection elements connected to the external terminals are integrated on the controller chip, and the second overvoltage protection elements connected to the connection terminals are mounted on the card substrate. The distances from the connection terminals are increased in order of the second overvoltage protection elements, controller chip, and plural memory chips, which are arranged like columns from one side of the card substrate to the opposing side thereof. Owing to this column-like arrangement, the second overvoltage protection elements for finally releasing the overvoltage are located closest to the connection terminals to which an overvoltage is applied, and the memory chips storing the data are located remotest, offering a high reliability from the standpoint of preventing electrostatic damage to the semiconductor chip and protecting the data.
In this case, too, the memory chips may be mounted on the card substrate in a manner of being stacked one upon the other with their positions being so deviated that the external terminals are exposed.
The arrangement of the memory chips and the controller chip mounted on the card substrate is not limited to the column-like arrangement only. When plural connection terminals are arranged along one side between the two neighboring sides of the card substrate, the memory controller is arranged with its lengthwise direction in parallel with the other side of the two neighboring sides, and plural memory chips are arranged in parallel in a direction nearly at right angles with the direction in which the connection terminals are arranged. The connection terminals exposed from the card substrate are connected to predetermined external terminals of the controller chip, the first overvoltage protection elements connected to the external terminals are integrated on the controller chip, and the memory chips are connected to the controller chip. With the connection terminals and the controller chip being arranged along the neighboring two sides of the card substrate, it is allowed to easily increase the density for mounting the memory chips or to increase the number of mounts. If the memory chips are arranged in parallel being divided into a first group in which the memory chips are stacked in a plural number with their positions being so deviated that the external terminals are exposed and a second group in which the memory chips are stacked in a plural number in the same manner, the height of the IC card can be suppressed. The second overvoltage protection elements connected to the connection terminals may be mounted on the card substrate along the direction in which the connection terminals are arranged.
[5] When an IC card is constituted by forming electrically conducting patterns on both surfaces of the card substrate, the electrically conducting patterns may be connected by using through holes that are penetrating through the card substrate. In this case, it is desired that the through holes are arranged outside the molded region that covers the semiconductor integrated circuit chip and the other surface of the card substrate. The molding that is executed while applying a pressure eliminates the probability in that the molding resin flows into the back side of the card substrate passing through the holes.
When the through holes are formed for the connection terminals exposed from the IC card, it is desired that the through holes are formed at positions deviated from the slide surfaces of the connection terminals. Even when the IC card is attached to, or detached from, the mounting slot, therefore, the terminals of the slot do not come into slide contact with the through holes and do not receive mechanical force, preventing such a probability that the patterns of the connection terminals are cracked from the through holes and are damaged.
The invention is concerned with an IC card in which plural connection terminals are exposed on one surface of a card substrate, a semiconductor integrated circuit chip is mounted on the other surface of the card substrate, predetermined external terminals of the semiconductor integrated circuit chip are connected to the connection terminals, first overvoltage protection elements connected to the external terminals are integrated on the semiconductor integrated circuit chip, and second overvoltage protection elements connected to the connection terminals are mounted on the other surface of the card substrate, and wherein the semiconductor integrated circuit chip, the second overvoltage protection elements and the other surface of the card substrate are covered with a metal cap. The metal cap can be formed by reducing a metal plate, by a forging method or by a die casting method. This provides a countermeasure against EMI (electromagnetic interference) compared to the resin cap, and helps accomplish the sealing by mechanical fastening and accomplish the cap-sealing at a high temperature. The resin cap may be blended with an electromagnetic wave-absorbing material such as ferrite, etc. To cope with ESD, electrically conducting particles such as carbon may be mixed.
An electrically conducting shielding pattern may be employed for the card substrate to relax the effect of electrostatic discharge that takes place near the card substrate. That is, the invention is concerned with an IC card in which plural connection terminals are exposed on one surface of a card substrate, and a semiconductor integrated circuit chip is mounted on the other surface of the card substrate, wherein predetermined external terminals of the semiconductor integrated circuit chip are connected to the connection terminals, first overvoltage protection elements connected to the external terminals are integrated on the semiconductor integrated circuit chip, second overvoltage protection elements connected to the connection terminals are mounted on the other surface of the card substrate, and an electrically conducting shielding pattern is formed on one surface of the card substrate except a region of the connection terminals, the electrically conducting shielding pattern being connected to the connection terminal for supplying ground power source or being connected to none of the connection terminals. The electrically conducting shielding pattern disperses the static electricity.
[6] From the standpoint of preventing electrostatic damage of when the IC card is handled in an unexpected manner by a person who is not familiar with, the IC card is provided on the surface thereof with an indication indicating a position where the IC card should be held by fingers (figure of a finger printed on a position at where the IC card should be held by fingers at the time of attachment or detachment), the IC card mounting a semiconductor integrated circuit chip permitting plural connection terminals to be exposed. Further, a notice is written on the surface of the IC card warning not to touch the connection terminals. Besides, a notice is written on the packing member packing the IC card warning not to touch the connection terminals of the IC card.
[7] The invention deals with a IC card giving attention to recovering the stored data, wherein plural connection terminals are exposed, plural memory chips and a controller chip for controlling the memory chips are mounted on a card substrate, the connection terminals are connected to a first group of external terminals of the controller chip, the memory chips are connected to a second group of external terminals of the controller chip, and data evaluation terminals connected to the second group of external terminals are formed on the card substrate.
In case the controller chip becomes no longer capable of executing the memory control due to electrostatic damage, access can be made directly to the memory chips from an external unit through the data evaluation terminals. Therefore, even when the controller chip is destroyed, the data remaining in the memory chips can be easily recovered.
The card substrate may further be provided with a control terminal for controlling the output terminal included in the second group of external terminals of the controller chip to assume a high output impedance state. The damaged controller chip that is placed in an undesired signal output state, can be easily relieved.
The controller chip may often be provided with a privacy protection mechanism for executing the encryption for the data that are written into the memory chips and for executing the decryption for the data read out from the memory chips. In this case, the data are recovered by the manufacturer of the IC card or by an authorized person by decrypting the data read out from the memory chips.
[8] The simplest method of recovering the data from the IC card having the data evaluation terminals, includes a first processing for placing the memory chips in a state where they cannot be controlled by the controller chip, and a second processing for reading out the data from the data evaluation terminals by controlling the memory chips. A data recovery method of when the controller chip has the privacy protection function, includes a first processing for controlling the output terminal included in the second group of external terminals of the controller chip to assume a high output impedance state, a second processing for reading out the data from the data evaluation terminals by controlling the memories, a third processing for decrypting the data read out by the second processing, and a fourth processing for writing the data decrypted by the third processing into another IC card.
Therefore, even in case the input circuit of the semiconductor integrated circuit chip is electrostatically damaged, the data that remain safe in the memory can be easily recovered.